How Does Bundler Work, Anyway? (RubyConf 2015)

We all use Bundler at some point, and most of us use it every day. But what does it do, exactly? Why do we have to use bundle exec? What's the point of checking in the Gemfile.lock? Why can't we just gem install the gems we need? Join me for a walk through the reasons that Bundler exists, and a guide to what actually happens when you use it. Finally, we'll cover some Bundler "pro tips" that can improve your workflow when developing on multiple applications at once.

Transcript

1. how does bundler
   work, anyway?
   

   View Slide

2. how does bundler
   work, anyway?
   

   View Slide

3. a brief (?) history of
   dependency management
   

   View Slide

4. André Arko
   @indirect
   

   View Slide

5. View Slide

6. therubyway.io
   

   View Slide

7. View Slide

8. View Slide

9. let’s share
   ruby code
   

   View Slide

10. Gemfile
    gem “foo”
    

    View Slide

11. Terminal
    $ bundle install
    

    View Slide

12. Terminal
    $ bundle exec foo
    

    View Slide

13. done!
    pretty cool, right?
    

    View Slide

14. but…
    what just
    happened?
    

    View Slide

15. iiiiit’s
    History
    ⚔
    Time
    

    View Slide

16. 1994 2000 2003 2009
    dependency timeline
    require setup.rb RubyGems Bundler
    

    View Slide

17. require
    it loads the codes
    

    View Slide

18. def require(filename)
    eval File.read(filename)
    end
    

    View Slide

19. i’m sure it’s fine
    run code twice?
    

    View Slide

20. $LOADED_FEATURES = []
    def require(filename)
    if $LOADED_FEATURES.include?(filename)
    return true
    end
    eval File.read(filename)
    $LOADED_FEATURES << filename
    end
    

    View Slide

21. probably fine too
    only absolute paths?
    

    View Slide

22. $LOAD_PATH = []
    def require(filename)
    full_path = $LOAD_PATH.first do |path|
    File.exist?(File.join(path, filename))
    end
    eval File.read(full_path)
    end
    

    View Slide

23. load paths are
    ⛄ pretty ❄ cool
    

    View Slide

24. but now we need…
    setup.rb
    

    View Slide

25. how do setup.rb?
    ruby setup.rb setup
    ruby setup.rb config
    ruby setup.rb install
    

    View Slide

26. use ruby libraries
    1. Find a cool library
    2. Download the library
    3. Untar the library
    4. Run `ruby setup.rb all`
    

    View Slide

27. no versions
    no uninstall
    but it’s fine, I’m sure
    

    View Slide

28. maybe a little bit
    incredibly tedious
    

    View Slide

29. what if you could…
    gem install
    gem uninstall
    gem list rails
    

    View Slide

30. bonus round!
    gem install rails -v 4.1
    gem install rails -v 4.2
    gem install rails -v 5.0
    
    

    View Slide

31. gem "rack", "1.0"
    require "rack"
    

    View Slide

32. $ rackup _1.2.2_ -p 3000
    

    View Slide

33. so many gems!
    100,000 gems
    1,000,000 versions
    

    View Slide

34. but gem apps don’t
    play well with others
    
    

    View Slide

35. welcome to the team
    here’s your machine
    we expect setting up
    to take a week
    

    View Slide

36. # config/application.rb
    […]
    config.gem “rack”
    config.gem “rails”
    config.gem “what?”
    […]
    

    View Slide

37. “why is this broken in production?”
    “dunno, it works on every developer machine”
    3 days of debugging later…
    “oh, look, one production server has frobnitz
    1.1.3, but the others have 1.1.4”
    “welp. that explains those exceptions ”
    

    View Slide

38. version conflicts
    gem install rails
    rails s
    cd ../other-project
    rails s
    
    

    View Slide

39. activation errors
    how common can
    they be, really?
    

    View Slide

40. $ rails s
    Gem::LoadError: can't activate
    rack (~> 1.0.0., runtime) for
    ["actionpack-2.3.5"], already
    activated rack-1.1.0 for
    ["thin-1.2.7"]
    activation errors
    

    View Slide

41. the moral
    runtime resolution
    install-time resolution
    

    View Slide

42. wait…
    how do we resolve
    at install-time?
    

    View Slide

43. View Slide

44. addressable (2.3.7)
    arel (6.0.0)
    bcrypt (3.1.10)
    binding_of_caller (0.7.2)
    debug_inspector (>= 0.0.1)
    builder (3.2.2)
    byebug (3.5.1)
    columnize (~> 0.8)
    debugger-linecache (~> 1.2)
    slop (~> 3.6)
    celluloid (0.16.0)
    Gemfile.lock
    

    View Slide

45. bundle install
    my old friend
    1. Read the Gemfile (and lock, if it's there)
    2. Ask RubyGems.org for a list of every gem we need
    2. Find gems allowed by the Gemfile that work together
    3. Write down those versions in the lock for future installs
    4. Install gems until every locked gem is installed
    

    View Slide

46. bundle exec
    everyone’s nemesis
    1. Read the Gemfile (and lock, if it's there)
    2a. Use locked gems if possible OR
    2b. Find versions that work to put in the lock
    3. Remove any existing gems the $LOAD_PATH
    4. Add each gem in the lock to the $LOAD_PATH
    

    View Slide

47. pro tip
    no more bundle exec!
    $ bundle binstubs rspec-core
    $ bin/rspec
    repeat as needed for other gems
    

    View Slide

48. was that the end?
    in a word, no.
    

    View Slide

49. I want YOU
    to contribute
    3
    @bundlerio
    team@bundler.io
    

    View Slide

50. or if you’re too busy,
    fund this work.
    http://rubytogether.org/join
    

    View Slide